The present invention relates to an improved construction of a single-rotation machine having internal axes with an external rotor and an internal rotor. These rotors are surrounded by a common casing circumferentially provided with an intake duct and an outlet duct, whereby as a result of the reciprocal engagement of the rotors they form working spaces with a variable volume sealed by sealing gap-forming rolling and/or sliding of alternating face regions of the rotors on one another and in which, based on its rotation axis, the internal rotor has radially inner circumferential surfaces, as well as transition surfaces between them.
In known machines of this type, the dimensioning of the sealing gaps between the two rotors constitutes an unsatisfactory compromise between the sealing losses and the frictional losses. Small sealing gaps, apart from correspondingly high frictional losses, also make high demands regarding the dimensionally correct manufacture and assembly.